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ACTH-dependent Cushing's syndrome — SCE Endocrinology MCQ

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HardPituitaryACTH-dependent Cushing's syndromeSCE Endocrinology

A 36-year-old woman has proximal myopathy, bruising and hypertension. Midnight salivary cortisol is repeatedly elevated and low-dose dexamethasone fails to suppress cortisol. ACTH is 9 pmol/L and pituitary MRI is normal. What is the most appropriate next investigation?

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Correct answer: D — Inferior petrosal sinus sampling

ACTH-dependent Cushing's syndrome with negative pituitary MRI requires specialist localisation, commonly inferior petrosal sinus sampling. Proceeding to adrenalectomy without localisation risks treating the wrong compartment. The pearl is that small corticotroph adenomas may be MRI-occult.

Reference: Endocrine Society Cushing's syndrome guideline, Society for Endocrinology guidance